Imaging optical unit

Abstract

An imaging optical unit comprises a plurality of mirrors for imaging an object field in an object plane into an image field in an image plane. An image-side numerical aperture is greater than 0.55. A ratio between an object/image offset and a meridional transverse direction is at least 0.5. A ratio between a working distance between the object plane and a reflection portion, closest to the object plane, of one of the mirrors and the meridional transverse dimension is at least 0.05. The working distance is at least 270 mm. This can yield an imaging optical unit, the use of which is relatively manageable in a projection exposure apparatus, such as for EUV projection lithography.

What is claimed is: 
     
         1 . An imaging optical unit, comprising:
 a plurality of mirrors configured to image an object field in an object plane into an image field in an image plane, wherein:   the imaging optical unit has an image-side numerical aperture greater than 0.55;   the imaging optical unit has an object/image offset between a separation plane and a center of the image field;   
       a center of the object field is located in the separation plane;
 the separation plane is perpendicular to a meridional plane of the imaging optical unit; 
 the imaging optical unit has a working distance between the object plane and a reflection portion, closest to the object plane, of one of the mirrors; 
 the working distance is at least 270 mm; 
 the imaging optical unit has a meridional transverse dimension between the separation plane and a reflection portion, furthest from the separation plane, of one of the mirrors; 
 a ratio of the object/image offset to the meridional transverse dimension is 0.76; and 
 a ratio of the working distance to the meridional transverse dimension is at least 0.05. 
 
     
     
         2 . The imaging optical unit of  claim 1 , wherein the object/image offset is at least 1500 mm. 
     
     
         3 . The imaging optical unit of  claim 1 , wherein the working distance is at least 275 mm. 
     
     
         4 . The imaging optical unit of  claim 1 , wherein the meridional transverse dimension is at most 4500 mm. 
     
     
         5 . The imaging optical unit of  claim 1 , wherein the imaging optical unit is an anamorphic imaging optical unit. 
     
     
         6 . The imaging optical unit of  claim 1 , wherein the imaging optical unit has a wavefront aberration of no more than 20 mλ. 
     
     
         7 . The imaging optical unit of  claim 1 , wherein the mirrors total at least eight. 
     
     
         8 . The imaging optical unit of  claim 1 , wherein the mirrors comprise at least four grazing incidence mirrors. 
     
     
         9 . The imaging optical unit of  claim 1 , wherein the mirrors comprise at least three normal incidence mirrors. 
     
     
         10 . The imaging optical unit of  claim 1 , wherein the object/image offset is at least 1500 mm, and the working distance is at least 275 mm. 
     
     
         11 . The imaging optical unit of  claim 10 , wherein the object/image offset is at least 1500 mm, and the working distance is at least 275 mm, and the meridional transverse dimension is at most 4500 mm. 
     
     
         12 . The imaging optical unit of  claim 1 , wherein the working distance is at least 275 mm, and the meridional transverse dimension is at most 4500 mm. 
     
     
         13 . The imaging optical unit of  claim 1 , wherein the mirrors total at least eight, and the mirrors comprise at least four grazing incidence mirrors. 
     
     
         14 . The imaging optical unit of  claim 13 , wherein the imaging optical unit is an anamorphic imaging optical unit. 
     
     
         15 . The imaging optical unit of  claim 13 , wherein the imaging optical unit has a wavefront aberration of no more than 20 mλ. 
     
     
         16 . The imaging optical unit of  claim 1 , wherein:
 the object/image offset is at least 1500 mm;   the working distance is at least 275 mm;   the meridional transverse dimension is at most 4500 mm;   the imaging optical unit is an anamorphic imaging optical unit;   the imaging optical unit has a wavefront aberration of no more than 20 mλ;   the mirrors total at least eight;   the mirrors comprise at least four grazing incidence mirrors; and   the mirrors comprise at least three normal incidence mirrors.   
     
     
         17 . An optical system, comprising:
 an imaging optical unit according to  claim 1 ; and   an illumination optical unit configured to illuminate the object field with illumination and imaging light.   
     
     
         18 . An illumination system, comprising:
 an optical system, comprising:   an imaging optical unit according to  claim 1 ; and   an illumination optical unit configured to illuminate the object field with illumination and imaging light; and   an EUV light source configured to produce the illumination and imaging light.   
     
     
         19 . An apparatus, comprising:
 an illumination system, comprising:   an optical system, comprising:   an imaging optical unit according to  claim 1 ; and   an illumination optical unit configured to illuminate the object field with illumination and imaging light; and   an EUV light source configured to produce the illumination and imaging light,   
       wherein the apparatus is a projection exposure apparatus for projection lithography. 
     
     
         20 . A method, comprising:
 using a projection exposure apparatus to project a structure on a reticle onto a light-sensitive material of a wafer,   wherein the projection exposure apparatus comprises:   an illumination system, comprising:   an optical system, comprising:   an imaging optical unit according to  claim 1 ; and   an illumination optical unit configured to illuminate the object field with illumination and imaging light; and   an EUV light source configured to produce the illumination and imaging light.